You might be able to find some info on the tractors used to transport "Mimi" and "Toutou" to Lake Tanganyika if you can get hold of Magee, Frank J. (October 1922). "Transporting a Navy through the Jungles of Africa in Wartime". National Geographic (XLII/4).

According to "Mimi and Toutou go forth", the "steam tractors" were bought in N Rhodesia. It would be reasonable to assume that these were Fowlers as that firm had an agencies in Kimberley and Johannesburg selling steam traction engines prior to the Boer War.

By the way, the map in the book shows the railway journey going via Johannesburg. There wasn't a direct railway line between Southern Rhodesia Johannesburg until the Rutenga rail link was completed in 1974, so this would have been quite an achievement at the time! The railway line from Cape Town to the Rhodesias went via Kimberley and Bechuanaland to Bulawayo. You then took a left turn and went off to Victoria Falls and over the bridge to Livingstone.

Edward Paice has some details in one of his books on the war in Africa. I think it's "Tip and Run" but I haven't read it for some time so I may be mistaken. I think the detail amounts to a photograph. Certainly there is at least one photo of Germans hauling a Konigsberg gun, using a couple of traction engines.

"Sometimes things that are not true are included in Wikipedia. While at first glance that may appear like a very great problem for Wikipedia, in reality is it not. In fact, it's a good thing." - Wikipedia.

Reading further into the book, the "steam tractors" are described as having a tall funnel and large wheels. This is confused by a later observation that their wheels were only 6" wide! The traction engines were also pulling 10-ton trailers.

In the book, it says: Shankland goes into some technical detail about these locomotives, which had been made by
Barrels of Thetford and Fowlers of Leeds. They could do 90 miles a day on a good road, apparendy,
and had been customised for working in Africa. ‘To guard against sparks setting the bush alight,’
writes Shankland, ‘they had ashpans specially constructed to hold water, and baffles and screens
fitted to the smoke-boxes. They seemed to have been well cared for, and every bit of brass about them
glowed like polished gold.’ Although Spicer later described them as ‘ordinary agricultural traction
engines’.
Spicer's view on anything can be taken with a ton of salt. On one occasion during their sea passage out to Cape Town, a passenger was giving other passengers a talk on the stars and constellations visible in the southern sky. Spicer got into an argument with the man about what was the Southern Cross, who eventually walked away - Spicer held himself to be a greater authority than the Astronomer Royal who was giving the talk!!

No description whatsoever is given of the truck which proceeded them on part of the journey.

The coverage of the event in the National Geographic found on the web does not have any pictures captured in it and the text says very little.
Tony